An Overview of Gas Turbines

Publisher Summary

The gas turbine is a power plant that produces a great amount of energy depending on its size and weight. The gas turbine has found increasing service in the past 60 years in the power industry among both utilities and merchant plants as well as the petrochemical industry throughout the world. The utilization of gas turbine exhaust gases, for steam generation or the heating of other heat transfer mediums, or the use of cooling or heating buildings or parts of cities is not a new concept and is currently being exploited to its full potential. The aerospace engines have been leaders in most of the technology in the gas turbine. The design criteria for these engines were high reliability, high performance, with many starts and flexible operation throughout the flight envelope. The industrial gas turbine has always emphasized long life and this conservative approach has resulted in the industrial gas turbine in many aspects giving up high performance for rugged operation. The gas turbine produces various pollutants in the combustion of the gases in the combustor. These include smoke, unburnt hydrocarbons, carbon monoxide, carbon dioxide, and oxides of nitrogen.

Gas turbine; simple-cycle gas turbine; compressor; regenerator; combustor; axial-flow turbine; radial-inflow turbine

The gas turbine is a power plant that produces a great amount of energy depending on its size and weight. It has found increasing service in the past 60 years in the power industry among both utilities and merchant plants, as well as in the petrochemical industry. Its compactness, low weight and multiple fuel application make it a natural power plant for offshore platforms. Today there are gas turbines that run on natural gas, diesel fuel, naphtha, methane, crude, low-BTU gases, vaporized fuel oils and biomass gases. The last 20 years have seen a large growth in gas turbine technology, spearheaded by the growth in materials technology, new coatings, new cooling schemes and combined cycle power plants. This chapter presents an overview of the development of modern gas turbines and gas turbine design considerations. The six categories of simple-cycle gas turbines (frame type heavy-duty; aircraft-derivative; industrial-type; small; vehicular; and micro) are described. The major gas turbine components (compressors; regenerators/recuperators; fuel type; and combustors) are outlined. A gas turbine produces various pollutants in the combustion of the gases in the combustor and the potential environmental impact of gas turbines is considered. The two different types of combustor (diffusion; dry low NOx, (DLN) or dry low emission (DLE)), the different methods to arrange combustors on a gas turbine, and axial-flow and radial-inflow turbines are described. Developments in materials and coatings are outlined.

The gas turbine is a power plant that produces a great amount of energy depending on its size and weight. The gas turbine has found increasing service in the past 60 years in the power industry among both utilities and merchant plants as well as the petrochemical industry throughout the world. Its compactness, low weight, and multiple fuel application make it a natural power plant for offshore platforms. Today there are gas turbines that run on natural gas, diesel fuel, naphtha, methane, crude, low-BTU gases, vaporized fuel oils, and biomass gases.

The last 20 years have seen a large growth in gas turbine technology. The growth is spearheaded by the growth of materials technology, new coatings, new cooling schemes, and the growth of combined-cycle power plants. This, with the conjunction of increase in compressor pressure ratio from 7:1 to as high as 45:1, has increased simple-cycle gas turbine thermal efficiency from about 15% to 45%.

Table 1-1 gives an economic comparison of various generation technologies from the initial cost of such systems to the operating costs of these systems. Because distributed generation is very site specific, the cost will vary and the justification of installation of these types of systems will also vary. Sites for distributed generation vary from large metropolitan areas to the slopes of the Himalayan mountain range. The economics of power generation depends on the fuel cost, running efficiencies, maintenance cost, and initial cost, in that order. Site selection depends on environmental concerns such as emissions, noise, fuel availability, size, and weight.

Gas Turbine Cycle in the Combined Cycle or Cogeneration Mode

The utilization of gas turbine exhaust gases, for steam generation or the heating of other heat transfer mediums, or the use of cooling or heating buildings or parts of cities is not a new concept and is currently being exploited to its full potential.

The fossil power plants of the 1990s and into the early part of the new millennium were the combined-cycle power plants, with the gas turbine being the center piece of the plant. It was estimated that, between 1997 and 2006, there was an addition of 147.7 GW of power. These plants have replaced the large steam turbine plants, which were the main fossil power plants through the 1980s. The combined-cycle power plant is not new in concept, since some have been in operation since the mid-1950s. These plants came into their own with the new high-capacity and high-efficiency gas turbines.

The new market place of energy conversion will have many new and novel concepts in combined-cycle power plants. Figure 1-1 shows the heat rates of these plants, present and future, and Figure 1-2 shows the efficiencies of the same plants. The plants referenced are the simple-cycle gas turbine (SCGT) with firing temperatures of 2400°F (1315°C), recuperative gas turbine (RGT), the steam turbine (ST) Plant, the combined-cycle power plant (CCPP), and the advanced combined-cycle power plants (ACCPPs), such as combined-cycle power plants using advanced gas turbine cycles, and finally the hybrid power plants (HPP).

Table 1-2 depicts an analysis of the competitive standing of the various types of power plants, their capital cost, heat rate, operation and maintenance costs, availability, reliability, and time for planning. By examining the capital cost and installation time of these new power plants, it is obvious that the gas turbine is the best choice for peaking power. Steam turbine plants are about 50% higher in initial costs of $800–$1000/kW than combined-cycle plants, which are about $400–$900/kW. Nuclear power plants are the most expensive plants. The high initial costs and the long time in construction make such a plant unrealistic for a deregulated utility.